Do we have / could we have / should we have
a clear long term (20 years) direction for text in C++?

ie the long term direction is unicode.
and/or specifically the long term direction is UTF8.
We expect everyone to use char8_t then? Or we expect char to become utf8
someday?
What do we want the long term future to look like?
deprecate std::string?

And then a list of short term stop-gap measures, like "we know we can't do
X yet,so we do Y for now".
Like we use char, but plan on switching to char8_t.
Or QoI escape hatches. etc.



On Sun, Sep 8, 2019 at 2:46 PM Corentin via Lib <lib_at_[hidden]>
wrote:

>
>
> On Sun, 8 Sep 2019 at 19:30, Tom Honermann <tom_at_[hidden]> wrote:
>
>> On 9/8/19 12:40 PM, Corentin wrote:
>>
>>
>>
>> On Sun, 8 Sep 2019 at 18:12, Tom Honermann <tom_at_[hidden]> wrote:
>>
>>> On 9/8/19 6:00 AM, Corentin via Lib wrote:
>>>
>>>
>>>
>>> On Sun, 8 Sep 2019 at 11:17, Corentin <corentin.jabot_at_[hidden]> wrote:
>>>
>>>>
>>>>
>>>> On Sun, 8 Sep 2019 at 09:52, Billy O'Neal (VC LIBS) <bion_at_[hidden]>
>>>> wrote:
>>>>
>>>>> > I agree that EGCS is the best option. That doesn't drag locale
>>>>>
>>>>>
>>>>>
>>>>> Because we don’t get to assume that we’re talking about Unicode at
>>>>> all, it absolutely drags in locale.
>>>>>
>>>>
>>>> Sorry, I should have been more specific.
>>>> There is a non-tailored Unicode EGCS boundary algorithm (but it can be
>>>> tailored)
>>>> I didn't mean to imply that text manipulation can be done without
>>>> knowing its encoding and never use "locale" to mean encoding.
>>>>
>>>> EGCS are only defined for text whose character repertoire is Unicode,
>>>> other encodings deal with codepoints
>>>>
>>>
>>>
>>> To be clear, the difference of whether the EGC algorithm is required to
>>> be tailored or not is that tailoring for all intent and purposes requires
>>> icu or something with CLDR, which restrict the platforms on which this
>>> can be implemented
>>>
>>> Tailoring is not relevant to this discussion.
>>>
>> It is - see https://unicode.org/reports/tr29/ "ch" is 2 EGCS in most
>> locales but in Slovak it's 1. I don't make the rules :D
>>
>> It isn't relevant in determining how we resolve this issue. If the
>> resolution is that field widths are measured in EGCs, then we've already
>> decided that the width is locale dependent and tailoring becomes an
>> implementation detail.
>>
>
> No, format decided to be locale-independent (for good reason) and applying
> locale specific behavior implicitly would be against that.
> I'n arguing for encoding specific behavior
>
>
>>
>> The locale dependency stems from the encoding itself being dependent on
>>> locale. Again, LANG=C vs LANG=C.UTF-8. If the specified behavior is
>>> encoding dependent (as it would have to be for field width to be a count of
>>> any of code points, scalar values, or EGCs), then it is also locale
>>> dependent (for char and wchar_t). Thus there is a trade off:
>>>
>>> 1. Either the behavior is locale dependent in which case, field
>>> widths could be specified such that they count code points, scalar values,
>>> or EGCs when the locale selects a Unicode encoding (and something else for
>>> non-Unicode encodings), or
>>> 2. The behavior is not locale dependent in which case, field widths
>>> can only be specified in terms of code units.
>>>
>>>
>> Agreed, but let me rephrase:
>>
>> Either a string is text and therefore we need and to know its encoding,
>> or it is a sequence of bytes (in the case of char)
>> I have an opinion about what we are dealing with in this context :D
>>
>> So your preference is for trade off #1 above and the cost is that
>> std::format is no longer locale insensitive even in the cases where a
>> std::locale argument is not provided.
>>
> It would be _encoding_ sensitive
> It would not change for example the decimal separator.
>
> When Unicode is involved - and even when it is not, it is I think
> important not to conflate locale and encoding even if C kinda amalgamates
> the two and derives one from the other.
>
>
>
>
>> Since I don't think field width works for alignment, even if EGCs are
>> used (see Henri's post - https://hsivonen.fi/string-length), I prefer
>> trade off #2.
>>
>> Tom.
>>
>>
>>
>> Recall that, unless there is a call to std::setlocale, all C and C++
>>> processes start with the locale set to "C"
>>>
>> Tom.
>>>
>>>
>>>
>>>
>>>>
>>>>
>>>>
>>>>
>>>>>
>>>>>
>>>>> Billy3
>>>>>
>>>>>
>>>>> ------------------------------
>>>>> *From:* Lib <lib-bounces_at_[hidden]> on behalf of Corentin via
>>>>> Lib <lib_at_[hidden]>
>>>>> *Sent:* Saturday, September 7, 2019 11:08:25 PM
>>>>> *To:* Library Working Group <lib_at_[hidden]>
>>>>> *Cc:* Corentin <corentin.jabot_at_[hidden]>; Victor Zverovich <
>>>>> victor.zverovich_at_[hidden]>; Tom Honermann <tom_at_[hidden]>;
>>>>> unicode_at_[hidden] <unicode_at_[hidden]>
>>>>> *Subject:* Re: [isocpp-lib] New issue: Are std::format field widths
>>>>> code units, code points, or something else?
>>>>>
>>>>>
>>>>>
>>>>> On Sun, Sep 8, 2019, 5:30 AM Tom Honermann via Lib <
>>>>> lib_at_[hidden]> wrote:
>>>>>
>>>>>> On 9/7/19 10:44 PM, Victor Zverovich wrote:
>>>>>>
>>>>>> > Is field width measured in code units, code points, or something
>>>>>> else?
>>>>>>
>>>>>> I think the main consideration here is that width should be
>>>>>> locale-independent by default for consistency with the rest of
>>>>>> std::format's design.
>>>>>>
>>>>>> I agree with that goal, but...
>>>>>>
>>>>>> If we can say that width is measured in grapheme clusters or code
>>>>>> points based on the execution encoding (or whatever the standardese term)
>>>>>> without querying the locale then I suggest doing so.
>>>>>>
>>>>>> I don't know how to do that. From my response to Zach, if code units
>>>>>> aren't used, then behavior should be different for LANG=C vs LANG=C.UTF-8.
>>>>>>
>>>>>> I have slight preference for grapheme clusters since those correspond
>>>>>> to user-perceived characters, but only have implementation experience with
>>>>>> code points (this is what both the fmt library and Python do).
>>>>>>
>>>>>> I would definitely vote for EGCs over code points. I think code
>>>>>> points are probably the worst of the options since it makes the results
>>>>>> dependent on Unicode normalization form.
>>>>>>
>>>>>
>>>>> I disagree. Code Units is the worse option. For me anything involving
>>>>> code units is a big red flag. I agree that EGCS is the best option. That
>>>>> doesn't drag locale, might be a bit involved for implementers in 20.
>>>>> I don't think specify EGCS for Unicode text and codepoints otherwise
>>>>> wouldn't be too difficult - implementation might be a bit challenging on
>>>>> some platforms in the 20 time frame but they could fallback to codepoints
>>>>> in the meantime. Not perfect but I think we need a good long term solution
>>>>> rather than a bad short term one
>>>>>
>>>>> Tom.
>>>>>>
>>>>>>
>>>>>> Cheers,
>>>>>> Victor
>>>>>>
>>>>>> On Sat, Sep 7, 2019 at 5:13 PM Tom Honermann via Lib <
>>>>>> lib_at_[hidden]> wrote:
>>>>>>
>>>>>>> [format.string.std]p7
>>>>>>> <https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Feel.is%2Fc%2B%2Bdraft%2Fformat%23string.std-7&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252854619&sdata=WsHw%2BM62uyiOBrr91P6W1GzwGe313EDe30bKN5i006Q%3D&reserved=0>
>>>>>>> states:
>>>>>>>
>>>>>>> The *positive-integer* in *width* is a decimal integer defining the
>>>>>>> minimum field width. If *width* is not specified, there is no
>>>>>>> minimum field width, and the field width is determined based on the content
>>>>>>> of the field.
>>>>>>>
>>>>>>> Is field width measured in code units, code points, or something
>>>>>>> else?
>>>>>>>
>>>>>>> Consider the following example assuming a UTF-8 locale:
>>>>>>>
>>>>>>> std::format("{}", "\xC3\x81"); // U+00C1 { LATIN CAPITAL
>>>>>>> LETTER A WITH ACUTE }
>>>>>>> std::format("{}", "\x41\xCC\x81"); // U+0041 U+0301 { LATIN CAPITAL
>>>>>>> LETTER A } { COMBINING ACUTE ACCENT }
>>>>>>>
>>>>>>> In both cases, the arguments encode the same user-perceived
>>>>>>> character (Á). The first uses two UTF-8 code units to encode a single code
>>>>>>> point that represents a single glyph using a composed Unicode normalization
>>>>>>> form. The second uses three code units to encode two code points that
>>>>>>> represent the same glyph using a decomposed Unicode normalization form.
>>>>>>>
>>>>>>> How is the field width determined? If measured in code units, the
>>>>>>> first has a width of 2 and the second of 3. If measured in code points,
>>>>>>> the first has a width of 1 and the second of 2. If measured in grapheme
>>>>>>> clusters, both have a width of 1. Is the determination locale dependent?
>>>>>>>
>>>>>>> *Proposed resolution:*
>>>>>>>
>>>>>>> Field widths are measured in code units and are not locale
>>>>>>> dependent. Modify [format.string.std]p7
>>>>>>> <https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Feel.is%2Fc%2B%2Bdraft%2Fformat%23string.std-7&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252864612&sdata=36WpbP64Oqoi4Pne9kFrEu6nauHLNr2VunnfkvdWcPY%3D&reserved=0>
>>>>>>> as follows:
>>>>>>>
>>>>>>> The *positive-integer* in *width* is a decimal integer defining the
>>>>>>> minimum field width. If *width* is not specified, there is no
>>>>>>> minimum field width, and the field width is determined based on the content
>>>>>>> of the field. *Field width is measured in code units. Each byte
>>>>>>> of a multibyte character contributes to the field width.*
>>>>>>>
>>>>>>> (*code unit* is not formally defined in the standard. Most uses
>>>>>>> occur in UTF-8 and UTF-16 specific contexts, but [lex.ext]p5
>>>>>>> <https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Feel.is%2Fc%2B%2Bdraft%2Flex.ext%235&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252864612&sdata=UyG%2Fr7BXuLAPAXP78ekpXS%2FWhqdeU2QCHTmTeBPjImQ%3D&reserved=0>
>>>>>>> uses it in an encoding agnostic context.)
>>>>>>>
>>>>>>> Tom.
>>>>>>> _______________________________________________
>>>>>>> Lib mailing list
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>>>>>>> Link to this post: http://lists.isocpp.org/lib/2019/09/13440.php
>>>>>>> <https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.isocpp.org%2Flib%2F2019%2F09%2F13440.php&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252874608&sdata=l4UxwaFExnxKireder%2F%2BAnU2mszZXMYatHrd2zGSSWQ%3D&reserved=0>
>>>>>>>
>>>>>>
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>>>>>> Link to this post: http://lists.isocpp.org/lib/2019/09/13446.php
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>>>>>>
>>>>>
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-- 
Be seeing you,
Tony